Leak Detection in London: Finding Hidden Leaks Fast

Engineer inspecting a concealed leaking pipe

If you suspect a hidden leak in your London property, do three things in order: turn off the water at the stop tap, check your meter to confirm water is escaping, then book a specialist to pinpoint the leak before anyone opens a wall or lifts a floor. Leak detection finds the exact spot using non-invasive tools, so the repair is small and targeted instead of a guess. This guide explains the signs, the first steps, the methods, who is responsible for which pipe, and what you can expect to pay.

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TL;DR

Unexplained damp, falling water pressure, noisy pipes or a higher metered bill are the classic signs of a concealed leak.
In an emergency, shut the stop tap, drain the cold taps, switch off heating and any immersion heater, then call a plumber.
Leak detection pinpoints the source with thermal imaging, acoustic listening or tracer gas, so repairs stay small.
You are responsible for the supply pipe from your boundary into the property and everything inside it. The water company looks after the mains.
UK guide prices for a survey run from about £80 to £1,600 depending on method and property. Ask for a fixed quote before work starts.

Signs you have a hidden leak
What to do the moment you find a leak
How professional leak detection works
Who is responsible for the leaking pipe?
What does leak detection cost in London?
Our perspective
Book leak detection with Evo Plumbers
A practical checklist before the engineer arrives
FAQ
Sources

Signs you have a hidden leak

Most leaks never announce themselves. Thames Water says over 95% of leaks are never seen by customers because they sit deep underground or behind finishes. So you look for the knock-on effects.

Outside the property

Wet or boggy patches in the garden during dry weather
Cracks in paving or a sunken area appearing
A noticeable drop in pressure at the taps

Those are the signs Thames Water lists for identifying a leak, and its household leakage code of practice adds reduced flow at the cold kitchen tap, noisy pipes and an unusually high metered bill.

Inside the property

The WaterSafe Register lists loss of pressure, rust, damp patches, mould on ceilings or walls, unusually lush or patchy vegetation, and a constant sound of flowing water in the pipes. In London flats, a stain on the ceiling below a bathroom is often the first thing a neighbour notices, so it is worth acting on early.

Check your meter

If you are on a water meter, it is the quickest test you have. South East Water’s customer-side leak guidance describes taking a reading, using no water for 30 minutes, then reading again. If the number has changed, water is escaping somewhere. Turn off the internal stop tap and read again to work out whether the loss is inside or outside.

Water meter test sequence for locating leaks

Southern Water adds a useful detail: after closing the stop tap, if the meter dial is still moving, the leak is between the meter and the stop tap. Thames Water notes that a rising meter reading can point to a leak on your supply pipe.

No meter? Your signs will be the physical ones above, or a bill that climbs for no reason you can explain.

What to do the moment you find a leak

A live leak is a race against damage. The WaterSafe Register’s emergency advice is clear and simple:

Turn off the water at the stop tap.
Open all the cold taps to drain the pipework and storage quickly. Do not turn on the hot taps.
Switch off the central heating and any electric immersion heater.
Call a plumber to find and fix the leak.

Southern Water’s guidance for a burst pipe goes further: soak up or block escaping water with towels, turn off the boiler, and switch off electrical fittings near the water. Water and electricity do not mix, so if water is reaching sockets or the consumer unit, keep clear and call an emergency plumber or electrician rather than reaching in.

Take photos of the damage before you clean up. They help with an insurance claim.

Check your insurance first

Thames Water advises checking your buildings insurance before arranging repairs, because some policies cover emergency plumbing and leaks and the insurer may help arrange and pay for the work. Many policies also include trace and access cover, which pays towards finding the leak and opening up the structure. Checkatrade’s cost guide makes the same point about asking your home insurer. Landlords and leaseholders should also check what the building’s block policy covers.

How professional leak detection works

When a leak is outside the house but still on your land, or indoors where you can neither see nor hear it, Thames Water says you need a leak detection specialist to locate it. The aim is simple: find the exact point, so the repair is one small opening rather than half a floor.

An engineer will normally start by talking through the symptoms, checking the stop tap and meter, and isolating sections of pipework. Then, depending on the situation, one or more of these methods comes in.

Method	How it works	Typically used for
Thermal imaging	Infrared camera shows temperature differences caused by hidden moisture	Leaks behind walls, ceilings and under floors
Acoustic detection	Sensitive microphones pick up the sound of escaping water	Buried supply pipes and pressurised pipework
Tracer gas	Harmless gas is introduced into the pipe and detected where it escapes	Small, stubborn leaks where other methods are inconclusive
Moisture meter and pressure testing	Confirms damp levels and whether a pipe holds pressure	Narrowing down which circuit is losing water

The first three are the methods Checkatrade describes as the common ones, with infrared suited to walls, ceilings and floors and tracer gas working without digging or lifting flooring.

No single tool solves every case. A heating leak under a screed behaves differently from a cold supply pipe running through a garden. That is why a good survey combines methods and ends with a clear answer: where the leak is, what caused it and what the repair involves.

Leak or blocked drain?

Sometimes the water you can see is not coming from a supply pipe at all. Thames Water says a blocked drain tends to show up as difficulty flushing, slow-emptying sinks and baths, and bad smells from drains. Water that cannot flow away can come back up and flood a home.

Water lingering in a slow-draining basin

A few clues suggest the blockage is in your own pipework: neighbours have no problems, your property does not share a drain with others, or only upstairs facilities are affected while downstairs works. If you think the blockage is in your drains, Thames Water advises contacting a plumber. If it looks like a drain problem rather than a leak, our drain unblocking service covers it, and the same visit can include a check for the underlying cause.

Who is responsible for the leaking pipe?

This decides who arranges and pays for the repair, so it is worth settling early. Using Thames Water’s pipe responsibility rules, which apply across most of Greater London:

The water company looks after the water mains and the communication pipe linking your supply pipe to the main. If you see a leak in the road or pavement, report it to them.
You, as the owner, are responsible for the supply pipe from your boundary into the home, plus all internal pipes, appliances and fittings.
Shared supply pipes carry joint responsibility among the owners for the shared section.
A leak can still be yours even if the pipe crosses a neighbour’s land or the road.

If the leak is on the supply pipe outside your home, the WaterSafe Register suggests checking with your water supplier, as they may be able to help with the repair. Parts of south and west London are served by other suppliers, so confirm yours from your bill.

The four-week clock

Once a leak on your property is confirmed, Thames Water expects you to arrange repair within four weeks. Miss that and it may serve a legal notice under Section 75 of the Water Industry Act 1991, after which it can no longer cover all the costs of the leak on a metered bill. So find it quickly and keep the written findings from the survey.

What does leak detection cost in London?

Prices vary because the work does. The UK range quoted by Checkatrade’s 2026 cost guide runs from £80 to £1,600 for standard leak detection, with infrared surveys from £150 to £1,000 and tracer gas from £250 to £2,000. London sits toward the upper end of national ranges because of access, parking and labour costs. These are guide figures for the UK, not our prices.

What moves the price:

The method needed. A thermal scan of a bathroom wall is quicker than tracing a buried pipe through a garden.
Access. Fitted kitchens, tiled floors, shared basements and communal pipework in purpose-built blocks all take longer.
Size and layout. A one-bed flat and a four-storey townhouse are different surveys.
Timing. Out-of-hours and emergency visits usually cost more than a planned appointment.
Repair on top. Detection finds the leak. Repair and making good are separate work, so ask what is included.

Our approach is to give a fixed quote before work starts, so you know the figure before an engineer begins. Our leak detection and plumbing pages do not publish a standard price, because it depends on the job, so get in touch for a fixed quote.

Our perspective

Most of the leaks we are called to were not dramatic when they began. A pinhole in a copper pipe behind a bath panel, a joint weeping under a floor, a supply pipe slowly losing water in a front garden. The damage comes from the weeks it goes unnoticed.

Our view is that detection should come before demolition. When the source is pinpointed first, the repair is smaller, the disruption is smaller and the conversation about cost is shorter. That is why we quote a fixed price before work starts: you should not be wondering what the final bill will be while your ceiling is wet.

London properties add their own complications: older pipework, flats stacked above one another, shared supply pipes and tight access. Having plumbing, drainage and gas engineers working together matters here, because a damp patch is not always a plumbing leak. It might be a drain problem, a heating leak or a gas appliance issue, and the person at your door needs to recognise which. Our engineers are Gas Safe registered, and we answer calls 24/7 because water does not wait for office hours.

If you are unsure whether what you have found is a leak, call us. Describing the symptoms is usually enough to know whether you need a survey or just a simple repair.

the author

Book leak detection with Evo Plumbers

If you have found damp, lost pressure or seen your meter moving with everything off, we can locate the leak and fix it. We cover London 24/7 with Gas Safe registered engineers and quote a fixed price before the work begins.

Evoplumbers

You can read about our leak detection service, or if the problem is urgent, use our emergency call out. We also cover specific neighbourhoods, including Fulham, Kensington, Battersea and Acton, with further pages for Wandsworth, Putney, Hammersmith, Chiswick and Notting Hill.

If the leak turns out to involve a heating system or boiler, the same team can handle boiler installation and gas works, so you are not coordinating several trades.

A practical checklist before the engineer arrives

A few minutes of preparation makes the survey faster and the findings clearer.

Note the meter reading and the time, so the engineer can see whether the number is moving.
Locate your stop tap and make sure it turns. In many London flats it is under the kitchen sink or in a shared riser, so find it before you need it in a hurry.
List the symptoms and when they started. A stain that appears only after a shower points somewhere different from one that grows constantly.
Clear access around the damp area, under the bath and to the boiler cupboard.
Tell the engineer about the neighbours. A leak affecting the flat below, or a shared supply pipe, changes who needs to be involved.
Photograph everything and keep your insurer’s number to hand.
Keep the written findings. They support an insurance claim and, if the leak was on your supply pipe, show you acted within the four-week window.

If you manage a rental, tell your tenant to report any damp, staining or pressure loss immediately. A small leak caught in week one is a minor repair. One left for a quarter can mean replastering, redecorating and a difficult conversation about who pays.

FAQ

How do I know whether the leak is inside or outside my home?

If you have a meter, record the reading, stop using water for 30 minutes and check again. Then close the internal stop tap and read once more. If the dial still moves, the leak is on the pipe between the meter and the stop tap. If it stops, the loss is inside the property.

Should I turn off the water straight away?

Yes. Close the stop tap, open the cold taps to drain the system, and switch off the heating and any immersion heater. Then call a plumber. Keep the hot taps off, and stay away from any electrics the water has reached.

Will the water company fix a leak on my property?

Only on its own assets: the mains and the communication pipe. The supply pipe from your boundary into the home and all internal plumbing are the owner’s responsibility. If you are unsure which part is leaking, a leak detection survey establishes it, and your supplier can confirm where their responsibility ends.

Does home insurance pay for leak detection?

Sometimes. Some buildings policies cover emergency plumbing and leaks, and many include trace and access cover for locating the source. Check your policy wording and call your insurer before authorising work, so you know what they need from the engineer’s report.

Can a blocked drain look like a leak?

It can. Slow-draining baths and sinks, bad smells and water coming back up point to a blockage rather than a supply leak. Drain unblocking is a different job from leak detection, so describe the symptoms when you call and the right engineer will attend.